Catheters that incorporate a plurality of spaced radiopaque markers can be used to, when positioned inside a patient and visualized using X-ray based techniques such as fluoroscopy, determine one or more dimensions of a vessel in which it is placed (e.g., diameter), or establish a magnification factor that the X-ray is using. An exemplary use of such a catheter can be to determine one or more dimensions of a vessel to help select an appropriately sized implant that is to be implanted within the vessel. These catheters may be referred to herein as sizing catheters or scaling catheters.
Sizing catheters that incorporate a plurality of axially spaced radiopaque markers are known. Standard sizing or scaling catheters incorporate the plurality of axially spaced radiopaque markers in such a way that the markers are disposed on the outside of an elongate shaft, such that the markers form an outer surface of the catheter at the locations of the markers. There is a risk that after the catheter has been advanced into the subject, the markers may become dislodged or disassociated from the elongate shaft, and remain inside the patient, subjecting the patient to serious complications. For example, the catheter may be advanced along a somewhat or very tortuous path, bending the catheter, which may result in forces being applied at the locations where the markers are coupled to the elongate shaft, which may cause the markers to become disassociated from the shaft.
Additionally, to deliver the sizing catheter to a target location inside the patient, sizing catheters may be advanced through an introducer catheter or sheath, which can include a hemostasis valve at the proximal end of the introducer. As the sizing catheter is advanced through the hemostasis valve, forces from the valve on the sizing catheter and radiopaque markers can destabilize the marker/shaft interface, thus increasing the likelihood that the markers can become dislodged inside the patient.
Sizing catheters and scaling catheters are needed that eliminate the risk that the plurality of radiopaque markers become dislodged from the catheter and remain in the patient.